Sexual Mimicry In Hyenas

  title={Sexual Mimicry In Hyenas},
  author={Martin N. Muller and Richard W. Wrangham},
  journal={The Quarterly Review of Biology},
  pages={3 - 16}
Genital masculinization in female spotted hyenas has been widely explained as an incidental consequence of high androgen levels. High androgen levels, in turn, were supposed to be favored because they led to adaptive aggressive behavior. Incidental androgenization is no longer a tenable hypothesis, however, because genital masculinization has been shown to proceed in the absence of androgenic steroids. Thus, an alternative hypothesis is required. The genitals of spotted hyena females are not… 
High maternal androstenedione levels during pregnancy in a small precocial mammal with female genital masculinisation
For both species plasma levels of androstenedione and testosterone in adults of both sexes, and in females during different stages of pregnancy were determined, indicating that high levels of this androgen may be involved in the differentiation of masculinized genitalia in female.
High maternal androstenedione levels during pregnancy in a small precocial mammal with female genital masculinisation
It is proposed that female genital masculinisation might be a side effect of early exposure to elevated levels of maternal androgens that might be selected for to speed up precocial development.
Exposure to naturally circulating androgens during foetal life incurs direct reproductive costs in female spotted hyenas, but is prerequisite for male mating
It is demonstrated that the reproductive costs of clitoral delivery result from exposure of the female foetus to naturally circulating androgens, and the same androgens that render an extremely unusual and laborious process even more reproductively costly in the female are apparently essential to the male's physical ability to reproduce with a normally masculinized female.
Development of the external genitalia: perspectives from the spotted hyena (Crocuta crocuta).
Male genital lobe morphology affects the chance to copulate in Drosophila pachea
Left lobe length affects the chance of a male to engage into copulation and the morphology of this primary sexual trait may affect reproductive success by mediating courtship signals or by facilitating the establishment of genital contacts at the onset of copulation.
Does the expression of a male plumage trait in female Kentish plovers (Charadrius alexandrinus) signal individual quality?
  • J. Amat
  • Biology, Environmental Science
    Journal of Ornithology
  • 2005
Kentish plovers (Charadrius alexandrinus) observed breeding in southern Spain expressed a plumage trait characteristic of males: the forecrown (frontal) black bar, which is suggested to be an epiphenomenon resulting from hormonal imbalances of females as they age.
Infanticide by females is a leading source of juvenile mortality in a large social carnivore
Of four hypotheses regarding the evolution of infanticide, the most support is found for the hypothesis thatinfanticide in spotted hyenas reflects competition over social status among matrilines.
Destruction of a conspecific nest by a female Superb Lyrebird: evidence for reproductive suppression in a bird with female-only parental care
High intra-sexual competition among female lyrebirds is revealed, which may provide an explanation for their elaborate vocal displays and propose that nest destruction may be a strategy that females use in protracted territorial negotiations spanning multiple breeding seasons.


Strategic concealment of sexual identity in an estrilid finch
  • N. Langmore, A. Bennett
  • Biology, Psychology
    Proceedings of the Royal Society of London. Series B: Biological Sciences
  • 1999
First experimental evidence is reported that sexual monomorphism enables strategic concealment of sex in long–tailed finches Poephila acuticauda, which suggests that in group–living species individuals might benefit by concealing their sex to reduce sexual competition.
Androstenedione may organize or activate sex-reversed traits in female spotted hyenas.
This study suggests that androstenedione may also produce the profound virilization of female spotted hyenas.
Androgens and masculinization of genitalia in the spotted hyaena (Crocuta crocuta). 3. Effects of juvenile gonadectomy.
It is suggested that postnatal phallic growth is largely independent of gonadal steroids, with oestrogenic facilitation of female-typical clitoral characteristics in spotted hyaenas.
Androgens and the Role of Female “Hyperaggressiveness” in Spotted Hyenas (Crocuta crocuta)
The results, and those from studies that have demonstrated that male and female hyenas experience similar levels of maternal androgens during fetal development, provide little support for a theory of selection for female dominance and hyperaggressiveness through enhanced secretion of androgens.
Plasma androgens in spotted hyaenas (Crocuta crocuta): influence of social and reproductive development.
The androgen profiles presented here suggest that the key to the behavioural dominance of female spotted hyaenas over males may lie with the neonatal developmental stages, rather than with the androgen patterns of adult animals.
Androgens and masculinization of genitalia in the spotted hyaena (Crocuta crocuta). 1. Urogenital morphology and placental androgen production during fetal life.
Investigating the timing of urogenital development and placental production of androgen during early and mid-gestation concluded that androgen is produced by the placenta and secreted into the fetal circulation from early in pregnancy when masculinization is first evident, before differentiation of the fetal ovary.
A mechanism for virilization of female spotted hyenas in utero.
The limited aromatase activity may allow the hyena placenta to convert high circulating concentrations of androstenedione to testosterone, which results in virilization of the fetal external genitalia and possibly destruction of fetal ovarian follicles.
Sex determination in marsupials: evidence for a marsupial-eutherian dichotomy.
  • M. Renfree, R. Short
  • Biology
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences
  • 1988
It is shown that extensive somatic sexual dimorphisms precede by many days the first morphological evidence of testicular formation, which does not occur until around the third day of pouch life, and strongly suggest that some sexually dimorphic somatic characteristics develop autonomously, depending on their genotype rather than the hormonal environment to which they are exposed.